Adhesives form a large part of daily activity for everyone, whether in the form of tape used to close a package or secure items together, bandages, envelopes, notepads, diaper tabs or any one of many other products in common use. The key requirements for adhesives are that they should have good cohesive and adhesive properties at conditions of use and application, whether by solvent or bulk casting. Usually these adhesives are prepared from a mixture of resin, copolymer and optionally a plasticizer to soften the adhesive and enhance tack.
Adhesives prepared from blends incorporated these components have very good adhesive and strength properties at room temperature and can be processed by conventional melt coating and extrusion techniques because of their good flow characteristics. Because of the excellent combination of properties exhibited by certain copolymers of a polydiene or a polyolefin and polystyrene, the use of such polymers for various pressure sensitive adhesive applications is growing in the industry.
Copolymers made from polystyrene and polydienes are widely used in the production of adhesives such as, for example, styrene/isoprene/styrene (SIS), polyethylene vinyl acetate (EVA), styrene/butadiene (SB), and styrene-ethylene butylene-styrene (SEBS), and the like. All of these copolymers whether formed by polymerization of polymer block or by random polymerization, are blended with tackifying resins in order to form the adhesive.
However, when copolymers are mixed with tackifying resins in order to form adhesives, many requirements and factors are important such as the ease with which the resin is blended with the copolymer and the control of the aggressiveness of the tack as well as the long term adhesive properties of the adhesive. Further, the adhesives industry has increased the demand for low softening point resins and market requirements dictate the desirability of resins which are not only liquid, i.e., softening point about 40.degree. C. or less, but that are light in color, normally a Gardner color less than 3. However, a resin would be considered to have sufficiently low color for some applications with a Gardner color of 6 or even 7.
While non-aliphatic resins having very low color exist even to the point of being water white, the use of these resins to blend with some copolymers to form pressure sensitive adhesives, resins containing some aromaticity, and light color, are desired. The presence of an oil plasticizer can cause detrimental results to substrates to which the adhesive is applied. Attempts to incorporate aromaticity, and thus compatibility with the styrene portion of copolymers, to the resin have generally caused an unacceptably high color level making the resulting adhesive unsuitable for various uses.
Accordingly, it is an object of this invention to provide a pressure sensitive adhesive incorporating a low softening point, from 0.degree. C. to about 40.degree. C., and light color aromatic-containing hydrocarbon resin.
It is a further object of this invention to provide adhesives in a binary or tertiary system of a copolymer and a low softening point resin having a light color even while including aromatic substituents to enhance adhesive properties.